This invention relates to a method and apparatus for controlling the register of a printing operation and at least one other operation performed on a web, and especially the register of colour separations printed on to a web, using a special pattern printed on the web.
The register of colour printing operations performed at different stations on a moving web has been controlled in the past by printing special register control marks either in a column at one edge of the web or else in gaps between the printed images. Where register control marks were printed in a column on one side of the web, generally to one side of each colour image, there was a significant wastage of space on the web. For adequate register control, it was necessary to provide substantial gaps between the colour images on the web when register control marks were printed in the regions between the colour images. A further disadvantage of known methods of register control is that the accuracy is limited by the stretching of the web between the region on which the colour image is printed and the region on which are printed the corresponding register control marks.